The invention is directed to an antenna system, and more particularly to an antenna system for modification of one or more sidelobe radiation patterns.
Antennas that radiate electromagnetic energy in the radio frequency spectrum are referred to as RF antennas. As a practical matter, earthly constraints make it impossible to achieve a perfect RF radiator.
RF antennas are typically metallic. During radiation, electromagnetic currents are present on the metallic surfaces of the antenna. These currents arise from multiple sources such as current spillover and diffraction from the main antenna radiating pattern. Additionally, a mismatch of the antenna feedpoint impedance with that of the transmission line characteristic impedance causes common mode RF currents on the metallic surfaces. The common mode currents and scatter can effect the overall radiation pattern of an antenna. Usually, the effect is undesired, taking the form of a sidelobe on an azimuthal plot of the antenna""s radiation pattern.
RF transmitting antennas for wireless communication systems, e.g., base station antennas, are becoming more and more common. In other words, the population density of RF transmitting antennas has steadily increased with no signs that the this trend will change any time soon.
The invention, in part, is a recognition of the problem that as population density of RF transmitting antennas increase, there is a point at which the side-lobe radiation pattern of one antenna can negatively affect one or more proximate antennas (be it a receiving antenna or another transmitting antenna), or other unintended structures or systems. Examples of such a situation include the placing of a wireless telephone base station transmitting antenna proximate to wireless mobile unit testing laboratories (where excessive ambient RF energy levels can cause the mobile test units to lock up) and the placing of wireless telephone base station antennas proximate to the RF communications equipment at an airport.
The invention, also in part, is a recognition that sidelobes in an antenna""s radiation pattern can be selectively modified through either constructive interference, destructive interference and/or RF absorption by adding additional structures to the base plate of an antenna.
The invention, also in part according to an embodiment, provides a side-lobe-modification antenna system comprising: an antenna including a base plate and an RF radiating arrangement attached to said base plate; and a side-lobe modification bracket having a first planar surface and a second planar surface intersecting the first planar surface, said second planar surface extending aside said radiating arrangement said radiating arrangement at an angle relative to the first planar surface, said first planar surface being parallel to and abutting said base plate.
The invention, also in part according to another embodiment, provides a side-lobe-modification antenna system comprising: antenna means including base plate means and RF radiating means attached to said base plate; and side-lobe suppression means, attached to said base plate means, for suppressing a side-lobe of said antenna means.
Additional features and advantages of the invention will be more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.